1. Field of the Invention
This invention relates generally to braking systems for manually operated pallet trucks and, particularly, to a normally engaged, manually disengagable brake for such a truck. The type of brake system disclosed hereinafter is colloquially referred to as a "dead man's brake", signifying a mechanism that would automatically actuate and engage a braking control in the absence of cognizant action.
2. Discussion of the Relevant Art
Manually operated pallet trucks have been in use for decades. Many innovations have been made in order to make these machines simpler and safer to use. U.S. Pat. No. 4,938,493, issued in July 1990, discloses state-of-the-art regarding manually operable pallet trucks. Therein, a modern, non-motorized pallet truck is defined possessing: a wheel-supported bed; a steering mechanism consisting of a steering tongue yoked to a steering column that is connected to a wheel assembly, the tongue also used in conjunction with a hydraulic subassembly for raising and lowering the truck platform; and several other devices used for jacking the bed, steering the entire assembly and accomplishing the functions set forth by the patentee, but not including the safety mechanism of the instant invention.
Another disclosure, U.S. Pat. No. 3,074,516, sets forth a hand truck that features a braking mechanism which is enabled when the operating handle thereof moves a pushrod into a locked position relative to the truck tongue. Movement of the tongue away from the vertical causes a brake shoe to contact both of the truck's steering wheels. This is a safety feature that engages the brake when manual effort is applied to move the tongue from a safe, rest position. Once the brake is cognitively released by the human operator, it will not automatically reapply itself should the operator fall or become disabled while the truck is in motion and, conceivably, under load. Having an objective, perhaps similar to that of U.S. Pat. No. 3,074,516, but functionally different, is the apparatus for braking a pallet truck and disclosed in Japan (laid open) 5-238393. Therein, there is disclosed a foot-operated brake that utilizes an over-center actuator to urge a shoe/pad into contact with a brake drum that is integrally formed within the wheel. The integral wheel-drum is used in the instant invention.
Because manual movement of heavy loads by use of pallet trucks can be fraught with danger, a need has been perceived for a device which would allow stabilization of the truck when not being moved as well as halting any motion should the operator control be lost suddenly. Such a safety device is embodied in the invention hereinafter disclosed.
3. Incorporation by Reference
To the extent that they disclose commonly known features and functions of manually operable pallet trucks, U.S. Pat. Nos. 3,608,922 and 3,074,516 are hereinafter incorporated by reference.